1. Field of the Invention
Embodiments of the present invention generally relate to post regulation of synchronous rectifier DC-to-DC converters and, more particularly, to post regulation of existing synchronous rectifiers in such DC-to-DC converters, independent of the main control loop.
2. Description of the Related Art
In modern power supply design, DC-to-DC converters are designed to have a very high gain-bandwidth product to provide high output current slew rate and minimize the capacitance for acceptable output voltage quality. The typical isolated power supply has one control regulator that operates the primary-side switching modulator to control line and load regulation, with either single or multiple control loops on the primary and/or secondary side of the transformer. However, isolated power supplies have a practical frequency limit that is from 2 to 10 times lower than the switching frequency to maintain operational stability, thereby limiting the maximum gain bandwidth desired for the fastest load voltage transient response. The maximum switching frequency is limited by the transformer magnetic materials and designs because of core losses and leakage inductances that effect reactive and switching losses. These losses should be kept low to provide high operating efficiencies and lower heat dissipation. Therefore, the switching frequencies and the gain-bandwidth are limited and cannot be as high as desired to provide a desirably fast load transient response.
In switch-mode power supplies and other types of DC-to-DC converters, secondary post regulators that are independent of the primary-side regulator are often placed in the secondary side of the transformer for faster load voltage transient response and better load regulation. These are usually linear regulators or pulse width modulated (PWM) buck regulators of various sorts, including magnetic amplifiers (mag amps). However, all these solutions add an additional conversion stage to the power supply that adds significant losses and requires the cost, size and complexity of another series regulator device, such as a power metal oxide semiconductor field effect transistor (MOSFET).